originally posted by: Snarl
I've looked ... and for the life of me, I've never been able to see definitive evolutionary change "from one species to another."
Probably because of a fundamental misunderstanding about how evolution works.
It isn't the case of a dinosaur giving birth to a chicken one day - the process is gradual and for every fossil we find and place in the evolutionary
tree, there are many more animals between them we will never find showing the gradual changes, although you can often find fossils of animals that are
clearly closely related.
The simplest way to describe evolution to anyone is this:
Imagine you have a cactus. It's in the desert, minding it's own business living off the seasonal rains. One day, through whatever means it is Cacti
reproduce, it disperses it's seeds.
Now, owing to errors in copying DNA, some of those seeds will be genetically different from their parent. Some will hold water better, some will hold
Then the climate changes - the rains become less frequent. Now, those Cacti that don't hold enough water perish, those that hold more water thrive.
This is natural selection.
Over the course of generations, more and more genetic mutations are introduced - some may affect the spines, some may affect the colouring, others may
affect the size of the flowers. Owing to the prevailing conditions (rain, insects, herbivores etc) those with the right mutations will survive, while
those who are poorly adapted will perish.
Eventually, after many generations, you will have a Cactus that is quite different from it's ancestor at the beginning of the story and is actually
an entirely different species adapted to it's environment.
The same works for animals.